Abstract: A method of setting the contact position between the operating cam and the roller for the air brake which includes a leading shoe and a trailing shoe respectively provided with a first roller and a second roller, a first lining and a second lining respectively provided on external surfaces of the leading shoe and the trailing shoe, a drum disposed on a circumference of the back plate, and the operating cam disposed to support the first roller and the second roller therebetween to rotate in a direction of expanding a gap between the leading shoe and the trailing shoe, includes setting the contact position between the operating cam and the second roller so that a direction in which the operating cam presses the second roller during braking is moved in a rotation direction of the drum when the vehicle moves backward thereof.